1. Field of the Invention
This invention relates to a granular fertilizer with a coating which degrades by light or oxidation. More particularly it relates to a granuler fertilizer with a coating comprising an ethylene-carbon monoxide copolymer. As to the product of the present invention, it is possible to adjust the dissolving-out rate of the fertilizer component, depending on the preparation conditions of the coating.
2. Description of the Related Art
In recent years, coated granular fertilizers obtained by encapsulating i.e. coating granular fertilizers to adjust the dissolving-out rate of fertilizer component have been developed and gradually come to be practically used.
Such coated granular fertilizers include mainly those of the following two types in the aspect of coating process:
.circle.1 those obtained by relatively thickly coating granular fertilizers with sulfur, wax or low molecular polyolefins and .circle.2 those obtained by relatively thinly coating them with high molecular materials such as polyolefins, etc.
However, the latter, i.e. those coated with high molecular materials, are superier in the aspect of the high adjustability of the dissolving-out rate and small damage to the coating at the time of handling, etc. On the other hand, the latter have raised the problem that, the coating step with the high molecular materials is technically not easy, and decomposition of the residualcoated material remaining after the product (coated granu-lar fertilizer) has been applied to soil requires a long time.
The present inventors have previously developed the technique of coating granular fertilizers with high molecular materials and controlling the dessolving-out rate of the fertilizer component and have applied for patent. For example, the present inventors disclosed a coating technique with a polyolefin resin solution and a technique of controlling the dissolving-out rate by the use of a surfactant) Japanese patent publication No. Sho 50-99,858/1975) and also disclosed a high level technique of controlling the dissolving-out rate by the simultaneous use of a polyolefin resin, an ethylene-vinyl acetate coplymer and a surfactant (Japanese patent publication No. Sho 60-37,074/1985). Further the present inventors disclosed a technique wherein by using a material obtained by further mixing and dispersing a mineral powder such as talc or sulfur powder in a polyolefin resin composition similar to the above, it is possible to not only control the dissolving-out rate of the fertilizer component, but also promote degradation or decomposition of the residual capsule i.e., the coating residue after use (application to soil) of granular fertilizer (Japanese patent publication No. Sho 60-3,040/1985 and Japanese patent application laid-open No. Sho 55-1,672/1980). However, the effectiveness of promoting the degradation or decomposition cannot yet be said to be sufficient. Thus, a higher level coating has been desired.